The present invention relates to a method and apparatus for controlling the environment within an enclosed space. More particularly, the present invention relates to an environmental control system for providing controlled ventilation of the interior space of an aircraft body, such that interior condensation and corrosion is reduced, cabin air quality is improved, the cabin can be humidified to healthy levels without increasing condensation and associated deleterious effects, and envelope fires can be directly suppressed and vented.
In the embodiments of the invention described below and illustrated in the appended drawings, the xe2x80x9cbodyxe2x80x9d of an aircraft is comprised entirely within the fuselage, and excludes the wings and tail surfaces, as well as those portions of the nose and tail cones which extend beyond the respective nose and tail pressure bulkheads. However, it will be understood that the present invention is equally applicable to other aircraft geometries (such as, for example flying wing and lifting body designs). Thus in general, and for the purposes of the present invention, the xe2x80x9cbodyxe2x80x9d of an aircraft will be considered to be that portion of the aircraft which is pressurized during normal cruising flight, and within which it is desirable to control the environment in order to enhance safety and comfort of passengers and crew.
For the purposes of the present invention, the body of an aircraft is considered to be divided into a cabin, one or more cargo bays, and an envelope which surrounds both the cabin and the cargo bay(s). The terms xe2x80x9ccabinxe2x80x9d and xe2x80x9caircraft cabinxe2x80x9d shall be understood to include all portions of the interior space of the aircraft which may be occupied during normal flight operations (i.e. the passenger cabin plus the cockpit) The term xe2x80x9cenvelopexe2x80x9d shall be understood to refer to that portion of the aircraft body between the cabin (and any cargo bays), and the exterior surface of the pressure shell (including any pressure bulkheads) of the aircraft. In a conventional jet transport aircraft, the envelope typically comprises inter alia the exterior fuselage skin; nose, tail and wing root pressure bulkheads; insulation blankets; wire bundles; structural members; ductwork and the cabin (and/or cargo bay) liner.
The term xe2x80x9cventilation airxe2x80x9d is defined as outside air typically introduced as bleed air from an engine compressor. For the purposes of this invention, xe2x80x9cventilation airxe2x80x9d shall be understood to be outdoor air brought into the cabin by any means, for example, engine bleed air, either with or without filtering. xe2x80x9cVentilation airxe2x80x9d does not include recirculation air or cabin air, filtered or otherwise reconditioned, which is supplied back into the interior space of the aircraft. For the purposes of this invention, xe2x80x9crecirculation airxe2x80x9d shall be understood to comprise air drawn from the interior space of the aircraft, possibly conditioned, and then returned to the cabin.
To facilitate understanding of the present invention, the following paragraphs present an outline of condensation/corrosion, air quality, and fire problems encountered in typical jet transport aircraft, and conventional measures taken to address such problems.
Aircraft are subjected to sub-zero temperatures (e.g., xe2x88x9250xc2x0 C.) when flying at cruising altitudes. While the aircraft skin is slightly warmer than outside air due to air friction, temperatures behind and within the insulation blankets (particularly adjacent the skin) cool to 0xc2x0 C. to xe2x88x9240xc2x0 C., depending upon flight duration and altitude. When cabin air passes behind the insulation, it can reach the temperature at which its moisture starts to condense (i.e., its dew point). Further cooling beyond this temperature will result in additional condensation (as liquid water or ice) on the skin and other cold sinks.
Cabin air circulates behind the insulation, drawn through cracks and openings by pressure differences created when the cabin is depressurized during ascent for example, and during flight by stack pressures (buoyancy effect). Stack pressures are created by density differences between the cooler air behind the insulation and the warmer air in front of the insulation. The density difference creates a slight negative pressure in the envelope (relative to the cabin) near the ceiling of the cabin and a slight positive pressure in the envelope near the floor of the cabin.
The effects of this condensation range from a simple nuisance through increased operation costs to decreased aircraft life. The more an airplane is used, the greater its occupant density and the lower the ventilation rate per person, the higher its potential for condensation problems. Cases have been reported of water dripping from the cabin paneling. Wetting of insulation increases thermal conduction and, over time, adds weight, increasing operating costs. This condensation increases the potential for electrical failure. It can lead to the growth of bacteria and fungi. It causes corrosion, leading to earlier fatigue failure and reduced aircraft life. Some estimates place capital and maintenance costs attributable to such condensation at up to $100,000 annually for larger, heavily utilized passenger aircraft.
Conventionally, passive measures have been used to cope with the envelope moisture problem. These include anti-corrosion coatings, drainage systems, and deliberately maintaining cabin humidity well below American Society of Air-Conditioning Engineers (ASHRAE) Standard recommended levels.
U.S. Pat. No. 5,386,952 (Nordstrom) teaches a method for preventing moisture problems by injecting dehumidified cabin air into the envelope. However, the installation of dehumidifiers, as taught by Nordstrom, increases electrical consumption, occupies additional volume, and adds dead weight. Thus in a recently published study (xe2x80x9cControlling Nuisance Moisture in Commercial Airplanesxe2x80x9d) Boeing Aircraft Company concluded that active dehumidification systems, such as those taught by Nordstrom, are not cost-effective, even though they can reduce moisture condensation within the envelope. Additionally, the dehumidification system taught by Nordstrom is incapable of addressing related cabin air quality issues, as described below.
Relative humidities above 65 percent which commonly occur in aircraft envelopes for even relatively low cabin humidities can support microbial growth under appropriate temperature conditions. Such growth can include Gram-negative bacteria. yeasts and fungi. Where sludge builds up anaerobic bacteria may grow, producing foul smelling metabolites. Saprophytic microorganisms provide nutriment for Protozoa. Exposure to aerosols and volatile organic compounds (VOCs) from such microbial growth can result in allergenic reactions and illness.
The relative humidity of outside air at typical cruising altitudes is frequently less than 1-2% when heated and pressurized to cabin conditions. Consequently, since cabin air normally is not humidified, on longer flights some passengers may experience dryness and irritation of the skin, eyes and respiratory system, while asthmatics may suffer incidences of bronchoconstriction. High air circulation velocities compound this problem. While humidification of the cabin air during flight would alleviate the xe2x80x9cdrynessxe2x80x9d problem, it would also exacerbate the potential for microbial growth and damp material off-gassing in the envelope.
Thus, although it would be of benefit for health purposes to maintain higher cabin air relative humidities which are within the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Standard, this is made impracticable by the envelope condensation problem.
Other air contaminants in aircraft causing sensory irritation and other health effects can originate from ventilation air, passengers, materials, food, envelope anti-corrosion treatments, envelope microbial growth, etc. Ventilation air contaminants originate outdoors and within the engine (when bleed air is used). Potential contaminant gases and particulate aerosols include:
combusted, partially combusted and uncombusted hydrocarbons (alkanes, aromatics, polycyclic aromatics, aldehydes, ketones);
deicing fluids;
ozone, possibly ingested during the cruise portion of the flight cycle; and
hydraulic fluids and lubricating oils, possibly originating from seal leakage within the engine.
Gas chromatography/mass spectrometry (GC/MS) head space analyses of engine lubricating oil (FIG. 9a), jet fuel (FIG. 9b), and hydraulic fluid (FIG. 9c) indicate some of the potential VOCs that might be found in aircraft ventilation air.
FIG. 8a shows a GC/MS plot of a ventilation air sample taken in a jet passenger aircraft during the cruise portion of the flight cycle (28000 ft and xe2x88x9234xc2x0 C.) The total concentration was 0.27 mg/m3 at a cabin pressure altitude of approximately 8000 ft. For comparison, ventilation air VOC concentrations for downtown buildings typically are less than a third of this concentration. VOCs identified include 3-methyl pentane, hexane, 3-methyl hexane, toluene, hexanal, xylene, and many C9-C12 alkanes. Additional compounds reported by other researchers include formaldehyde, benzene and ethyl benzene. Many of the compounds in the jet fuel (FIG. 9b) can be seen in this ventilation air sample. The total VOC (TVOC) concentration was 0.27 mg/m3 at a cabin pressure altitude of approximately 8000 ft. Of this some 0.23 mg/m3 could have a petroleum (combustion source). The TVOC concentration is equivalent to a TOC exposure of 0.36 mg/m3 at sea level. In comparison, urban residential ventilation air TVOC concentrations are typically less than one-third this aircraft ventilation air concentration (i.e.,  less than 0.03 mg/m3), and building room air TVOC concentrations typically are less than 0.5 mg/m3. One postulate for the high VOC concentrations found in aircraft is that periodic incidents of lubricating oil leakage produce aerosols which enter the ventilation system and progressively coat the interior surfaces of the supply ducts. This coating, in turn, could sorb VOC""s ingested during taxi from the exhaust of other aircraft. These VOC""s may subsequently be released into the cabin during flight.
Contaminated ventilation air increases ventilation rate requirements to achieve any particular space concentration target. For example, a ventilation rate with TVOCs=0.36 mg/m3 must be three times higher than one with TVOCs=0.036 mg/m3 to maintain a room TVOC concentration of 0.5 mg/m3.
Cabin air contaminants can originate from materials and, possibly microbial growth in the envelope as well as from cabin furnishings, food and passengers. Contaminants in the envelope enter the cabin when cabin air is circulated behind the insulation drawn there by envelope stack pressures and by decreasing cabin pressures (for example, during ascent).
FIG. 8b shows a GC/MS plot of envelope air in an aircraft parked when the temperature in the air space between the skin and insulation was approximately 35xc2x0 C. The total (TVOC) concentration was 22 mg/m3. Of this, some 21 mg/m3 had a petroleum source and 0.6 mg/m3 could have had a microbial source. VOCs from one source of these envelope contaminants, an anti-corrosion treatment, is illustrated in FIG. 9e. This head space sample was taken at xe2x88x925xc2x0 C., a temperature representative of the temperature behind the insulation during the early portions of cruising flight. This anti-corrosion treatment emitted many of the compounds seen in the envelope and the ventilation air, plus a number of cycloalkanes and aliphatics not seen in the other samples. FIG. 9d shows the head space GC/MS plot of a general purpose cleaner (2-butanone or methyl ethyl ketone) used on this aircraft. This compound was also identified in the envelope, engine oil, ventilation air and anti-corrosion treatment samples.
When the envelope is cooled in flight or warmed on the ground, envelope material off-gassing and sorption of contaminant gases change. For example under ideal conditions, the deposition of VOCs of interest behind the insulation could increase a hundred-fold for temperature decreases over the typical flight cycle temperature range.
Condensation of higher molecular weight compounds at higher concentrations may occur when the envelope is cooled. For example, the maximum concentration of dodecane (a compound found in the ventilation air and anti-corrosion treatment samples), at xe2x88x9240xc2x0 C. is 0.26 mg/m3.
One implication of the above is that during the ascent and the early portions of the cruise flight cycle while the envelope is still relatively warm, envelope VOCs could pose an air quality problem for passengers. Another implication is that cabin air VOCs will be deposited (sorbed) in the envelope when it is cold, particularly during later stages of the cruise portion of the flight cycle. For example, both ventilation air VOCs (FIG. 8a) and the cabin cleaner VOC (FIG. 9d) can be found in the envelope air sample (FIG. 8b).
Some aircraft have high efficiency particulate filters (HEPA) filters which will remove human microbial aerosols that enter the circulation system. Some have catalytic converters to remove ozone. Very few have sorbent air cleaners to remove ventilation-air and cabin VOCs.
In the case of a fire, thermal and electrical insulation systems in the envelope as well as other materials in the cabin can undergo pyrolysis and burning, generating toxic smoke and combustion products. Conventionally, this problem is addressed by employing fewer combustible materials, and using hand-held containers with non-toxic fire suppressants. Currently, insulation is under review in this regard with a prevention program potentially involving more than 12,000 commercial aircraft.
Under any cabin fire emergency, the objective is to exhaust the smoke from the cabin while suppressing the fire. There is currently no method in place to directly suppress or extinguish fire and/or pyrolysis within the envelope. Nor is there any effective means of preventing smoke within the envelop from penetrating into the cabin. Furthermore, exhaustion of air from the cabin is usually via grilles at the floor. which undesirably enhances smoke circulation throughout the cabin.
U.S. Pat. No 4,726,426 (Miller) teaches a method of fire extinguishment in aircraft cabins using ventilation ducts in communication with the cargo fire extinguishment system. However, this system does not address envelope fires and/or pyrolysis, or the health and safety problems associated with exposing, passengers to potentially lethal combinations of fire suppressants and their combustion products in combination with fire and smoke.
It is an object of the present invention to provide an environment control system that overcomes the above-noted deficiencies in the prior art.
It is a further object of the present invention to provide an environment control system capable of inhibiting moist cabin air from contacting cold surfaces of the envelope, thereby reducing moisture condensation within the envelope, and associated xe2x80x9crain-in-the-planexe2x80x9d, electrical failures, corrosion, microbial growth, and dead weight.
It is a further object of the present invention to provide an environment control system capable of reducing infiltration of smoke from the envelope into the interior cabin space, thereby increasing passenger and crew safety during an in-flight fire situation.
It is a further object of the present invention to provide an environment control system capable of improving cabin indoor air quality (IAQ) by at least partially removing contaminants from ventilation air prior to entering the cabin.
Accordingly, an aspect of the present invention provides an environment control system for an aircraft including at least a pressure shell, an interior space including one or more of a cabin and a cargo hold, an envelope extending between the interior space and the pressure shell and a liner disposed between the interior space and the envelope. The environment control system comprises an envelope air distribution system having a plurality of nozzles located at spaced intervals and adapted to distribute an envelope air stream within the envelope in such a manner as to at least partially offset stack effect pressures.
Another aspect of the present invention provides an environment control system for an aircraft including at least a pressure shell, an interior space including one or more of a cabin and a cargo hold, an envelope extending between the interior space and the pressure shell and a liner disposed between the interior space and the envelope. The environment control system comprises an envelope air distribution system adapted to supply an envelope air stream to the envelope; and one or more flow-blockers adapted to at least partially block a flow of air within the envelope.
Another aspect of the present invention provides an environment control system for an aircraft including at least a pressure shell, an interior space including one or more of a cabin and a cargo hold, an envelope extending between the interior space and the pressure shell and a liner disposed between the interior space and the envelope. The environment control system comprises an envelope air distribution system adapted to supply an envelope air stream within the envelope; and sealing means adapted to at least partially seal the liner against leakage of air between the interior space and the envelope.
In embodiments of the invention, one or more flow-blockers are provided, and adapted to at least partially block a flow of air within the envelope. The envelope air distribution system may include a plurality of nozzles located at spaced intervals and adapted to distribute the envelope air stream within the envelope in such a manner as to at least partially offset stack effect pressures. Sealing means adapted to at least partially seal the liner against leakage of air between the interior space and the envelope may be included.
In embodiments of the invention, the envelope air distribution system may further include: at least one envelope supply duct; and at least one respective ventilation air branch line in communication with the envelope supply duct and one or more respective nozzles.
An insulation blanket may be disposed within the envelope between the liner and the pressure shell. At least one nozzle may be a shell-side nozzle adapted to inject envelope air between the insulation jacket and the pressure shell. At least one nozzle may be a cabin-side nozzle adapted to inject envelope air between the insulation jacket and the liner.
In embodiments of the invention, an air supply is adapted to generate the envelope air stream. The air supply may include an air supply duct adapted to conduct bleed air from a compressor stage of an engine of the aircraft into the body of the aircraft as ventilation air. The air supply may also include an airflow control device adapted to divide the flow of ventilation air into the envelope air stream and a cabin air stream. An air conditioner pack adapted to cool the ventilation air may also be included. The airflow control device may include at least one valve adapted for controlling the envelope air stream and the cabin air stream to maintain a predetermined pressure difference between the cabin and the envelope.
In embodiments of the invention, a cabin air distribution system is adapted to distribute the cabin air stream within the interior space of the aircraft body. The cabin air distribution system may include: an air conditioner communicating with the airflow control device for receiving at least a portion of the cabin air stream, and adapted to condition the cabin air stream to create cabin supply air; and a cabin supply air duct adapted to direct the cabin supply air into the cabin. The air conditioner may be adapted to control the relative humidity of the cabin supply air, e.g. to maintain a cabin relative humidity level in excess of 20%.
In embodiments of the invention, the sealing means is adapted to limit a leakage area of the cabin liner such that a predetermined pressure difference between the interior space and the envelope can be maintained at a predetermined minimum ventilation rate. The minimum ventilation rate may be about 0.55 lbs per passenger or less. The leakage area may be equivalent to about 73 cm2) per passenger, or less.
In embodiments of the invention, at least one flow blocker is arranged to reduce stack effect air flows within the envelope. The flow-blockers may be arranged to divide the envelope into one or more sections. In such cases, the envelope air distribution system may be adapted to control envelope ventilation within a section independently of other sections. At least one section may formed by dividing at least a portion of the envelope longitudinally, e.g. to form at least one section within a crown of the envelope. At least one section may be formed by dividing the envelope laterally, e.g. to form at least one section within a cockpit portion of the envelope. At least one section may formed by dividing the envelope both longitudinally and laterally, to form at least one section within the envelope proximal a food preparation area of the cabin.
In embodiments of the invention, a return air control unit is capable of drawing a return air stream from a selected one of the interior space and the envelope The return air control unit may include a housing, a first opening defined in the housing and in communication with the envelope, a second opening defined in the housing and in communication with the interior space, and a damper capable of selectively closing one of the first opening and the second opening. An outflow valve may be adapted to divide the return air stream into an exhaust air stream and a recirculation air stream, the exhaust air stream being vented out of the aircraft, and the recirculation air stream being supplied back to the cabin. The recirculation air stream may be supplied to the cabin via an air conditioner.
In embodiments of the invention an anti-corrosion/VOC sorption treatment is applied to an interior surface of the aircraft structure within the envelope. The anti-corrosion/VOC sorption treatment may be formulated to provide acceptable characteristics of: adhesion to metal surfaces; hydrophobic; low flammability; and low off-gassing at typical envelope temperatures during cruising flight. The anti-corrosion/VOC sorption treatment is formulated to: resist solidification within the aircraft envelope; sorb ventilation air VOCs at typical envelope temperatures during cruising flight and desorb said ventilation air VOC""s at warmer temperatures substantially without hysteresis.
In embodiments of the invention, a fire suppression system is provided in communication with the envelope air distribution system. The fire suppression system is preferably capable of releasing a flow of chemical fire suppressant into at least the envelope air distribution system when smoke or fire is detected in the envelope. The fire suppression system and the envelope air distribution system may be adapted to cooperate to flood at least a portion of the envelope with the chemical fire suppressant. The fire suppression system may include a container of chemical fire suppressant, a supply line in communication with the container and the envelope air distribution system for conducting the chemical fire suppressant between the container and the envelope air distribution system and a valve capable of controlling a flow of chemical fire suppressant from the container. The chemical fire suppressant may be any one or more of Halon, carbon dioxide, nitrogen and other fire suppressant agents, or mixtures, of these.
A further aspect of the present invention provides a method of controlling the environment within an aircraft including at least a pressure shell, an interior space including one or more of a cabin and a cargo hold, an envelope extending between the interior space and the pressure shell, and a liner disposed between the interior space and the envelope, the method comprising a step of distributing an envelope air stream within the envelope through a plurality of nozzles so as to at least partially offset stack effect pressures.
Another aspect of the present invention provides a method of controlling the environment within an aircraft body including at least a pressure shell, an interior space including one or more of a cabin and a cargo hold, an envelope extending between the interior space and the pressure shell, and a liner disposed between the interior space and the envelope. The method comprises the steps of: distributing an envelope air stream within the envelope; and providing one or more flow-blockers within the envelope and adapted to at least partially block a flow of air within the envelope.
Another aspect of the present invention provides a method of controlling the environment within an aircraft body including at least a pressure shell, an interior space including one or more of a cabin and a cargo hold, an envelope extending between the interior space and the pressure shell, and a liner disposed between the interior space and the envelope. The method comprises the steps of: distributing an envelope air stream within the envelope; and at least partially sealing the liner against leakage of air between the envelope and the interior space, such that a predetermined pressure difference between the envelope and the interior space can be maintained at a predetermined minimum ventilation rate.
In embodiments of the invention the envelope air stream is distributed within the envelope through a plurality of nozzles so as to at least partially offset stack effect pressures. At least a portion of the envelope air stream may be injected into a space between the pressure shell and an insulation jacket. At least a portion of the envelope air stream may be injected into a space between an insulation jacket and the liner.
In embodiments of the invention, a return air stream may be drawn from selected one of the envelope and the cabin. The return air stream may be divided into an exhaust air stream and a recirculation air stream, the exhaust air stream being vented from the aircraft and the recirculation air stream being supplied back to the cabin.
In embodiments of the invention, a supply air stream is divided into the envelope air stream and a cabin air stream. The cabin air stream is supplied to the cabin; and the envelope air stream and the cabin air stream are controlled to maintain a predetermined pressure difference between the cabin and the envelope.
In embodiments of the invention the cabin air is humidified, and the humidified cabin air is supplied to the cabin.
In embodiments of the invention, during a cruising portion of a flight cycle. the predetermined pressure difference is selected such that the envelope is at a higher pressure than the cabin. In such cases, the return air stream may be drawn from the cabin. Similarly, a portion of the return air stream can be vented out of the aircraft, and a remaining portion of the return air stream recirculate back into the cabin.
In embodiments of the invention, during a taxi and ascent portion of a flight cycle, the predetermined pressure difference is selected such that the envelope is at a lower pressure than the cabin. In such cases, the return air stream can be drawn from the envelope, and substantially all of the return air stream may be vented out of the aircraft.
In embodiments of the invention, during an in-flight fire and/or pyrolysis within the envelope or in the cabin, the predetermined pressure difference is selected such that the envelope is at a lower pressure than the cabin. In such cases, at least a portion of the envelope can be flooded with a chemical fire suppressant, and the cabin air stream may include substantially all of the total flow of ventilation air. The return air stream may be drawn from the envelope, and substantially all of the return air stream vented out of the aircraft.
In embodiments of the invention, during ground operations of the aircraft, the return air stream is drawn from the envelope and substantially all of the return air stream is vented out of the aircraft. In such cases, the ventilation air stream may be heated to accelerate volatilization of VOCs and any moisture within the envelope.
The environment control system of the invention can be incorporated into new aircraft construction, or installed as an upgrade or retrofit in an existing aircraft.